Mollusc

Humanity's oldest enemy, and perhaps more commonly known as the Martians. They were left behind when the humans fled their home solar system. For humanity, they're a long passed threat. Another chapter to be read and skipped over in it's great history. And the Molluscs intend to shatter this perception.

During the 1898 invasion of Terra, the Mollusc's superior technology nearly destroyed the entirety of the continent of Europa. However, they proved vulnerable to Terra's microbiology, having destroyed their own aeons ago. Due to this, their weaker immunities caused them to succumb to the bacterial plague.

With the help of the Mi-Go, they have long since adapted to this weakness.